Clinoptilolite, one of common naturally yielding zeolites, has been industrially used as gas adsorbents. For use as gas adsorbents, clinoptilolite has been used with ion exchange sites thereof being exchanged with suitable ions. As such a clinoptilolite, ion-exchanged clinoptilolites which are obtained by ion exchange of naturally yielding clinoptilolite with different ions have been reported, such as a calcium-exchanged clinoptilolite (for example, see Patent Literature 1), a magnesium-exchanged clinoptilolite (for example, see Patent Literature 2), and a strontium-exchanged clinoptilolite (for example, see Non-Patent Literature 1).